Trump’s attack against the Alphabet Inc unit follows a string of grievances against technology companies, including social media Twitter Inc and Facebook Inc, which he has accused of silencing conservative voices, and Amazon.com Inc, which he has said is hurting small businesses and benefiting from a favorable deal with the U.S. Postal Services. He frequently berates news outlets for what he perceives as unfair coverage.

Google denied any political bias, saying in a statement that its search engine is “not used to set a political agenda and we don’t bias our results toward any political ideology.”

Trump said in several tweets on Tuesday that Google search results for “Trump News” were “rigged” against him because they showed only coverage from outlets like CNN and not conservative publications, suggesting the practice was illegal.

“I think Google is really taking advantage of our people,” Trump said on Tuesday in the Oval Office. “Google, and Twitter and Facebook, they are really treading on very, very troubled territory, and they have to be careful. It’s not fair to large portions of the population.”

Facebook declined to comment. Twitter did not comment when asked for a response. In congressional testimony, both companies have denied engaging in partisan censorship.

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Neither Trump nor the White House detailed how or under what legal justification they would use to probe Google.

Trump’s economic adviser, Larry Kudlow, later told reporters that the White House was “taking a look” at Google, saying the administration would do “some investigation and some analysis,” without providing further details.

Earlier this summer, the new Republican chair of the Federal Trade Commission, Joseph Simons, said the agency would keep a close eye on big tech companies that dominate the internet. In a previous investigation, the FTC decided that Google was likely justified in developing a search function that harmed other companies.

In June Representative Keith Ellison, a Democrat, asked the Federal Trade Commission to investigate Google’s alleged anticompetitive behavior in the online search and advertising markets.

Congressional sources cautioned that it may be difficult for Trump to find a way to probe Google about news search results, and that Congress is unlikely to pass any applicable laws.

U.S. member of Congress Ted Lieu, a Democrat, said in a tweet directed at Trump that such restrictions on Google would violate the U.S. Constitution: “If government tried to dictate the free speech algorithms of private companies, courts would strike it down in a nanosecond.”

TRUMP’S CRITICISM OF MEDIA

While the exact science behind Google searches on the internet is kept secret, its basic principles are widely known to be generated with a variety of factors measured by the company’s algorithms.

The factors Google uses to determine which websites appear first in search results include how often that page is linked to on other sites, the use of keywords, the popularity and respectability of the news site, and personal browsing history of the person conducting the search.

Highly trafficked and cited websites like CNN.com and NYTimes.com, two of the most Trump’s most frequent targets, often appear first in search results.

Trump’s accusation of bias on the part of Google comes as social media companies have suspended accounts, banned certain users and removed content as they face pressure from the U.S. Congress to police foreign propaganda and fake accounts aimed at disrupting American politics, including operations tied to Iran and Russia.

Companies such as Facebook and Twitter have also been pressed to remove conspiracy driven content and hate speech.

FILE PHOTO: FILE PHOTO: U.S. President Donald Trump listens to a question during an interview with Reuters in the Oval Office of the White House in Washington, U.S. August 20, 2018. REUTERS/Leah Millis/File Photo

Tech companies have said they do not remove content for political reasons.

Some Republican U.S. lawmakers have also raised concerns about social media companies removing content from some conservatives, and have called Twitter’s chief executive to testify before a House of Representatives panel on Sept. 5.

Earlier this month, Alphabet’s YouTube joined Apple Inc and Facebook in removing some content from Infowars, a website run by conspiracy theorist Alex Jones. Jones was also temporarily suspended on Twitter.

Reporting by Susan Heavey; Additional reporting by Ken Li in New York and Chris Sanders in Washington; Editing by Frances Kerry and Richard Chang